1. Field of the Invention
The present invention relates to insulated tubing, in particular, steel pipe having a fiberglass liner with an insulating material in the space therebetween.
2. Prior Art
Conventional downhole oil drilling techniques typically require (as shown in FIG. 1) the use of a casing C positioned in a producing well H, a production tubing T positioned within the casing C and a packer P which centers the casing C and retains the production fluid F adjacent to the opening of the production tube T. Transport lines are pipes used to transport hydrocarbon fluids. In cold environments, hot hydrocarbon fluids passing through the production tubing T or transport lines contain paraffin and asphaltenes. As the hot fluids containing the paraffin and asphaltenes cool in the cold environment, the paraffin and asphaltenes solidify and form deposits in the production tubing or transport line. These deposits must be periodically cleaned out. Typically, the oil production process must be shut down to allow cleaning of the paraffin and asphaltene deposits.
Accordingly, a need remains for a device and method for transporting hot hydrocarbon fluids in a cool environment to prevent premature solidification of paraffin and asphaltenes entrained in the hydrocarbon fluids.
This need is met by the insulated tubing of the present invention. The insulated tubing includes an outer steel pipe and an inner fiberglass liner. The fiberglass liner is sized to provide a defined annulus between the liner and the pipe. The annulus between the liner and the pipe is filled with an insulating composition including a cementitious material and an additive. The additive lowers the K value of the cementitious material, thereby increasing the insulating properties of the insulating composition. Preferably, the cementitious material includes Portland cement and the additive includes glass beads or the like produced from fly ash, preferably on the order of about 30 microns in size. The amount of additive included in the insulating material and the radial thickness of the annulus filled with the insulating composition are dependent on the insulating needs of the tubing in a particular oil production environment.
The annulus between the liner and the pipe is maintained at approximately a constant thickness around the circumference of the liner by a plurality of sets of spacers positioned at spaced apart locations along the length of the liner. The constant thickness provides for substantially equal thermal insulation around all of the pipe. Each set of spacers preferably includes three spacers positioned equidistantly around the outer surface of the liner. The spacers are preferably formed in a U-shape or C-shape and are secured to the outside of the liner by a strap passing over each of the spacers. Preferably, each spacer includes a slot defined therethrough which accepts the strap to prevent the strap from slipping off the spacers. The spacers may be formed from a length of polyvinyl chloride (PVC) tubing cut longitudinally to create an elongated U-shaped member. The height of the spacers is dependent upon the size of the annulus between the liner and the tubing.
The insulated tubing is prepared by first attaching the spacers with the strap around the outside of the liner at defined intervals, preferably every four to five feet, with the length of the spacers being about four to five inches. The liner is inserted into the tubing and the insulating composition is pumped into the annulus between the liner and the tubing. The insulating composition flows in the gaps between the spacers. The insulating composition hardens and forms an insulating layer between the liner and the tubing.
A complete understanding of the invention will be obtained from the following description when taken in connection with the accompanying drawing figures wherein like reference characters identify like parts throughout.